Epoxy resins are a well established class of curable (thermosettable) compositions which find utility in a myriad of applications. The curing of epoxy resins is effected by a wide range of curing agents, for example, the primary and secondary polyamines including the aliphatic amines, cycloaliphatic amines and aromatic amines; dicarboxylic acids and anhydrides thereof; aromatic hydroxyl containing compounds: imidazoles; guanidines; urea-aldehyde resins, melamine-aldehyde resins and alkoxylated derivatives thereof; amidoamines, and various combinations thereof. In many of the applications served by epoxy resins, it would be desirable to improve one or more of the physical and/or mechanical and/or thermal properties of the cured products.
Corley et al. in U.S. Pat. No. 4,791,154 (issued Dec. 13, 1988) discloses the use of aromatic azopolyamine curing agents with epoxy resins. A compound included as an azopolyamine curing agent is ##STR1## while the diglycidyl ether of 4,4'-dihydroxydiphenyl is included as one of the epoxy resins suitable for use.
Dhein et al. in U.S. Pat. No. 4,762,901 (issued Aug. 9, 1988) discloses the preparation of polymeric networks having superstructures via polymerization of liquid crystalline materials within the liquid crystalline temperature range of said materials. Certain specific epoxy resins and certain specific diamines containing a liquid crystalline moiety are described in the teachings, with a specific example of the glycidyl ether of 4'-hydroxyphenyl-4-hydroxybenzoate cured with 4'-aminophenyl-4-aminobenzoate being disclosed.
The present invention provides a method for improving one or more of the physical and/or mechanical and/or thermal properties of cured epoxy resins by incorporating one or more specific rodlike mesogenic structures into the epoxy resin and one or more of any rodlike mesogenic structures into the polyamine curing agent used therewith. These epoxy resin and polyamine curing agent compositions exhibit ordering of the molecular chains in the melt phase. This morphology is susceptible to flow induced orientation during processing which can result in enhanced unidirectional mechanical properties. This is not possible to any extent with conventional (non-mesogenic) epoxy resin and curing agent compositions. The simultaneous presence of rodlike mesogenic moieties in the epoxy resin as well as the polyamine curing agent allows for a greater concentration of said moieties in the cured products thereof and thus a higher susceptibility to induced orientation.